The invention relates to thermal condition sensor systems. More specifically, the invention is directed to a sensor system for monitoring the thermal condition of operating equipment, such as aircraft engines.
Early detection of fire and over-temperature conditions is essential for satisfactory operation of aircraft and other equipment. Unfortunately, current sensor systems are limited in reliability and maintainability as a consequence of their basic design and method of operation. Conventional sensors must be placed in contact with the source of heat, thereby subjecting the sensors to thermal and mechanical degradation. In aircraft engine nacelles, for example, fire and overheating are detected by closed loop systems which are placed directly on the engine. The presence of abnormally high temperatures is sensed by changes in the electrical resistance of enclosed wires or changes in the pressure of gases. At other locations, the presence of abnormal conditions is often recognized indirectly utilizing smoke detectors and/or visual explosion detectors.
Some of the disadvantages of conventional sensor systems include (1) generation of spurious indications and false alarms that reduce confidence in the sensor system, (2) negligible monitoring of on-going conditions and lack of recognition of incipient problems, (3) reduced reliability due to exposure to extreme temperature and vibration, (4) difficult and costly maintenance, removal, and replacement, (5) inaccurate indications caused by local temperature excursions, and (6) slow and insensitive smoke detection.
Optical radiometric devices exist which determine temperature and thermal conditions by detection and analysis of emitted optical radiation, but no completely satisfactory method has been provided for reliable fire and over-temperature detection. Conventional radiometric devices provide limited discrimination between thermal sources, respond to only a single environmental condition, and are not rugged enough for use in severe environments--such as in the vicinity of an aircraft engine to monitor engine operation.
Thus, there is a real need for a thermal condition monitoring system which is rugged enough to be used in severe environments, which need not be placed in contact with the source of heat, which is sensitive to multiple environmental conditions, and which does not give false alarms.